This invention relates to a power steering system for a boat, and more particularly to a power steering system for a boat which is adapted to accurately detect steering torque of a steering wheel to permit a drive motor to generate appropriate assistance force.
A power steering system which has been conventionally used for a boat is generally constructed in such a manner as shown in FIG. 1. More particularly, the conventional power steering system includes a steering wheel 103 mounted at the front portion of a boat 101 which is provided at the rear portion thereof with an outboard motor 105 including an engine 107 and a screw propeller 109. The power steering system also includes a steering arm 111 which is connected to the outboard motor 105 and pivotally mounted on the boat 101 through a shaft 112 in a manner to be pivotally movable about the shaft 112. To the steering arm 111 is connected a lever 113. Between the steering wheel 103 and the lever 113 is arranged a wire 115 in a manner to extend therebetween, which is enclosed in a wire tube 117. On the lever 113 is fixedly mounted a rack 119, which is engaged with a pinion 121. The power steering system further includes a drive motor 123, which is arranged so as to be engaged with the pinion 121 through a speed reducer 125.
Also, the conventional power steering system includes a torque sensor 127 arranged at the portion of the wire 115 adjacent to the outboard motor 107, which is adapted to detect steering torque of the steering wheel 103 to generate a detection signal s127, which is then supplied to a controller 129. The controller 129 then generates a control signal s129 depending upon the so-supplied detection signal s127, which is then supplied to the drive motor 123, resulting in the drive motor 123 generating assistance force which corresponds to the steering torque. Thus, the drive motor 123 generates assistance force depending upon the steering torque of the steering wheel, resulting in desired steering operation. This leads to a significant decrease in steering force.
The outboard motor 107 is provided with a revolving speed sensor 131 for detecting a speed of the boat, a neutral switch 133 and a reverse switch 135, which respectively supply signals s131, s133 and s135 to the controller 129. Also, to the controller 129 is supplied electric power from a power supply or battery 137.
However, in the conventional power steering system constructed as described above, the wire 115 is arranged in the wire tube 117. This causes frictional resistance to occur between the wire 115 and the wire tube 117 when the wire is actuated, which prevents the steering torque from being accurately transmitted to the torque sensor 127.